additive fertilizer

So ive been looking into alg a mic and it sounds like id be mad not to be using some sort of seaweed extract in my feed. Boosts disease resistance, cold resistance, encourages microbes in the soil and has loadsa auxins and other goodies. Unfortunately I cant get my hands on some for this grow...

Which one would you pick if you had to stick to only one choice? Is it the bloom booster, fulvic acid, cali-mag, silica, vitality booster, molasses, kelp......